1. Field of Invention
The present invention relates to a gun trigger assembly. More particularly, it relates to a trigger assembly for installation into a submachine gun for converting said gun from a fully automatic to a semi-automatic firing weapon and which further prohibits said semi-automatic firing weapon from being converted back to a fully automatic firing weapon.
2. Description of the Prior Art
Machine guns are well known in the prior art. Their history can be traced back to 1718 when James Puckle invented what he called the “Defence Gun” which mounted on a tripod and included a large revolver with a cylinder behind a single barrel. The cylinder was turned manually and it could fire 63 shots in seven minutes.
The American Civil War saw more advancement in the art when Wilson Agar produced the Coffee Mill gun for the Union Army. This gun had a wheeled frame carrying 24 rifle barrels. Once the gun was loaded, a single percussion cap was placed on a nipple on the iron frame and fired by a hammer. The flash passing through the frame ignited all 24 cartridges.
Thereafter, Richard Gatling invented the infamous “Gatling Gun” made up of six barrels mounted in a revolving frame. This weapon was first used by the United States Army and subsequently by most major armies of Europe.
Inspired by the success of the Gatling Gun, others were encouraged to enter this emerging field of weapon production. In 1879 the Gardner machine gun was shown for the first time. This weapon had two-barrels that were operated by a crank which loaded and fired each barrel in turn. The feed system was a grooved strip into which the rims of a box of cartridges could be slid, after which the box was removed. This gun could fire up to 10,000 rounds in less than 30 minutes.
Finally, a weapon thought to be the grandfather of all modern machine guns was introduced by Hiram Maxim in 1885. He used the energy of each bullet's recoil force to eject the spent cartridge and insert the next bullet, a general principle still used today in the art. The Maxim machine gun could fire until an entire belt of bullets was used up, thereby discharging upwards of 500 rounds per minute. The success of this invention inspired other inventions and improvements upon machine guns such as the German Army's Maschinengewehr and the Russian Pulemyot Maxima which were both based on Maxim's invention. The advent of the Maxim machine gun eclipsed manually operated “crank” style mechanical guns and set the stage for later developments.
By the outbreak of the First World War in 1914, the machine gun was an integral part of all warring nations. But most were still mounted upon tripods, carts or vehicles and required more than one operator. Improvements were therefore still needed and desired. The idea of a single operator weapon, a so called “machine rifle,” which could fire a high volume of bullets was desired by the World's armies. Attempts to produce such a weapon were being made during WWI, but with limited success. One such example is the Browning Automatic Rifle or “BAR” developed by John Browning in 1917. The BAR was a gas-operated, air-cooled, magazine-fed weapon. It chambered the standard service round of that period, the .30-06 Springfield. It weighed about 16 to 19 pounds empty, depending upon the model. The magazine was a detachable box-type with a capacity of only 20 rounds. It was used by the US military through the Korean War where it served as a squad's light machine gun. It could be mounted on bi-pod or shot from a hip or shoulder position. Frequently, an assistant would carry extra ammunition for the operator. However, the assistant was not needed to fire the weapon. And, like other emerging single operator machine guns that could be carried by one person, the barrel was fixed. Although effective, its long profile left much to be desired in a more convenient weapon for WWI and a need existed for a better single operator machine gun.
General John Thompson wished to address this need and set out to build a different type of gun, one that is now referred to as a submachine gun. The designs of such weapons came from a desire to make a machine pistol, one that didn't use rifle rounds. Pistol designs had seen the advent of highly reliable weapons such as the 1911 design for the .45 caliber, used extensively by the US military at that time and for another 80 years thereafter.
Thompson knew that the heart of any machine gun lied in its breech locking and feeding mechanisms. Thompson was well aware of the designs used in other guns of the day, but none was appropriate for his design. Recoil actuated systems were popular in the heavy and medium machine guns of the era, but these used many moving parts that were heavy and prone to failure. The Recoil system uses the rearward thrust of a movable barrel to unlock the breech, eject the spent cartridge case, insert a fresh cartridge, re-lock the breech and fire the next round. Gas actuated systems had many of the same drawbacks as recoil systems. A gas system employs a small vent hole drilled into the barrel that bleeds off some of the high pressure gasses that propel the bullet out through the barrel. The vented gas pressure is routed back to the breech area where it drives a piston that performs the same unlocking, ejection, loading, re-locking and firing sequence as a recoil operated gun. The third system, used mostly in semi-automatic handguns, such as the 1911 pistol, employed a technique referred to as “Blowback.” These guns relied on the propellant gas pressure to literally ‘blow’ the bolt rearward. This action powered the sequence of ejecting and loading the next round. Guns using the blowback process are simple because they do not have a locking breech. They depend on the forward inertia of a heavy bolt, driven by a recoil spring, to keep the breech closed at the point of peak chamber pressure. The blowback system seemed to be the ideal choice for use in a lightweight machine gun because of its simplicity, lack of heavy moving parts and reliability. But in practice, it is only usable with low powered pistol ammunition, such as the .45 caliber. High power rifle ammunition creates much higher chamber pressure that overcomes any inertia in the bolt, blowing it back prematurely and thus causing cartridge cases to be ejected during peak pressure, exposing the operator to the hazards of ruptured brass and explosive gasses.
To solve this problem, Thompson sought to find a way to make a simple but practical breech lock. He uncovered across U.S. Pat. No. 1,131,319 to Blish entitled a “Breech Closure for Firearms.” This is essentially a breech locking mechanism that could be used on a blowback operated firearm. The lock delays the blowback of the bolt until the chamber pressure has diminished to an acceptable level. This use lead to the final production of the Thompson Submachine Gun. This weapon uses a .45 caliber pistol round and can accept either a 100 or 50 round drum or a 30 or 20 round box magazine. The gun was originally nick-named the “Trench Broom” because it was envisioned by General Thompson that a single user rushing an entrenched position, like those of WWI, could attack and fire upon the entire trench, thereby inflicting a high rate of causalities, or “sweeping it clean.” Although the US military was slow to accept the weapon, it finally ordered a small number of the weapons that arrived at the docks of New York just as WWI ended in 1918.
The gun underwent some changes and adaptations during the period between WWI and WWII, but its original design remained essentially the same. Federal enforcement agencies and local police forces began to use the Thompson during this period to combat organized crime. In fact, the United States Postal Service was one of the first purchasers of the Thompson Submachine Gun. When WWII came along, the US military finally realized the importance of such a weapon and more than one and one half million of the weapons were eventually produced. During WWII, methods were used to make the gun more cost effective to produce. But, the original design never really changed.
The Thompson Submachine Gun operates on a very simple principle. It is an open bolt weapon. That is, when the weapon is ready to fire, the bolt and working parts are held to the rear. When the trigger is pulled the bolt goes forward, feeding a round from the magazine into the chamber and firing it. Like any other self-loading design without an external power supply, the action is cycled by the energy of the exploding round; this sends the bolt back to the rear, ejecting the empty cartridge case and preparing for the next round. The expanding gas of the exploding cartridge fires the bullet and pushes the bolt backward against a recoil spring. So long as the trigger is pulled, a sear will not engage a small indent in the bolt and will continue permitting bullets to be fired in an automatic mode. Once the trigger is released, it acts upon the sear which catches the small indent and prevents the bolt from moving forward against a new cartridge.
It has been unlawful since 1934 (The National Firearms Act) for civilians to own any type of machine gun without special permission from the U.S. Treasury Department. This of course includes the Thompson. Machine guns are now subject to a $200 tax every time their ownership changes from one federally registered owner to another and the gun must be registered with the Bureau of Alcohol Tobacco and Firearms (BATF) in its National Firearms Registry. So long as a person follows this procedure, ownership of existing machine guns is legal. Newly manufactured machine guns however are no longer available for purchase by the general public even with BATF registration and payment of the Treasury tax. Only military and law enforcement can purchase such new weapons now.
Even though existing machine guns can be legally owned in the US, many people simply do not feel comfortable owning such a weapon, or are unfamiliar with the registration and tax process or can simply not afford the cost of a classic WWII firearm, such as the Thompson Submachine Gun. Accordingly, some companies offer replicas of these firearms. And in fact, a replica of the Thompson Submachine Gun, which only fires in a single fire mode, can be purchased. Karr Arms offers such a replica. Unfortunately, the quality of these replicas is extremely poor. Collectors of classic WWI and WWII era firearms are disinterested from owning these inferior replicas.
Accordingly, a need exists for a gun such as the Thompson Submachine Gun to be available to a collector of vintage firearms at a reduced cost. These guns should be available as a semi-auto carbine to avoid the cost of purchasing transferable Class III guns. Further, these guns, if converted from a fully automatic to a semi-automatic firing weapon, need to exist in their semi-automatic configuration such that they are not capable of being converted back to a fully automatic firing weapon unless converted from a registered Class III weapon.